The invention relates to a sewing machine in accordance with the preamble of claim 1.
A rotational speed sensor is required for the operation of an electronically-controlled sewing machine, which is used for regulating the engine speed, for one, and at least one position sensor is furthermore employed, with the aid of which the angular position of the main shaft, and therefore the position of the needle bar, is determined.
A device for a sewing machine, called a pulse sensor, is known from DE 36 00 938 C1, which contains three concentrically arranged scanning tracks with a multitude of scanning markers on a screen disk, wherein the latter is arranged inside of the sewing machine housing on a shaft which rotates with the main shaft of the sewing machine. The outer one of the three scanning tracks is assigned to a speed sensor. By means of this assignment, a maximum number of scanning markers which can be scanned per unit of time is achieved, if the narrowest possible width of the scanning markers is utilized. Since the quality of regulation of the number of revolutions increases with an increasing number of scanning pulses available per unit of time, there are two options for increasing the quality of regulation, namely to increase the diameter of the screen disk and the corresponding scanning track and in this way to increase the number of scanning markers, and/or to drive the screen disk at a rotational speed which is greater in comparison with the main shaft of the sewing machine.
Since generally there is only little space available inside the sewing machine housing, it would be a solution to house at least the scanning track assigned to the speed sensor, or the screen disk, on the motor shaft either inside the motor housing or in the immediate vicinity of the motor housing.
An electric motor used for operating a sewing machine is known from DE-OS 2 227 116, which is flanged to the outside of the machine housing and is in a driven connection with the main shaft of the sewing machine by means of a coupling. Inside its housing, in the area of the coupling, the motor contains a fan wheel, which is driven by the motor shaft, and in the opposite end area a speed sensor and two position sensors at an axial distance. Even though the axial distance between the speed sensor and the two position sensors is small, there is a noticeable increase of the motor housing in the axial direction because of the three sensors being housed there. Such a step could possibly not be realizable in connection with a built-in motorxe2x80x94such as is customary with household sewing machinesxe2x80x94because of the restricted space conditions in the sewing machine housing.
The object of the invention is to arrange the speed sensor, and at least one position sensor, of a sewing machine, which is driven by means of an electric motor having a fan wheel, in such a way that, on the one hand, a large number of scanning markers per unit of time is available for the regulation of the number of revolutions and, on the other hand, its space-saving housing is assured. The object is attained by means of the characterizing features of claim 1.
Because of the step of combining the fan wheel of the motor and the screen disk of the speed sensor into a multi-functional wheel, and therefore to design a component of the motor which is provided anyway in such a way, that it performs a second additional function, the axial structural length of this motor is not increased in spite of the now integrated speed sensor.
Since moreover the at least one control segment disk of the position sensor is not arranged in or on the motor, but on the main machine shaft, or on a shaft driven synchronously with it, and therefore the structural length of the motor is not also affected by the position sensor, the motor embodied in accordance with the invention is particularly suited as a built-in motor.
By means of the further development in accordance with claim 2, wherein the fan wheel has an outer ring and the screen disk is arranged in the form of a toothed ring on the circumferential Side of the ring, it is possible to arrange a maximum number of scanning markers embodied as teeth, or tooth gaps.
If the motor is in driven connection with the main machine shaft by means of a belt drive, it is possible in accordance with claim 3 to embody the belt pulley assigned to the motor shaft as a component of the multi-function wheel.
Since in connection with an indirect drive, i.e. a drive by means of a belt drive, or possibly also a toothed gear, of the sewing machine, the motor shaft generally rotates at a higher speed than the main machine shaft, it is possible in this way to further increase the number of scanning markers available per unit of time.
A concrete measure for the secure fastening of the multi-function wheel is recited in claim 4.